Secondary batteries, which are easy to apply to various product groups and have good electrical energy characteristics such as high energy density, are widely used for electric vehicles (EVs) or hybrid vehicles (HVs), driven by electric driving sources, as well as portable devices.
The secondary batteries are capable of repeatedly charging and discharging by electrochemical reactions, which may reduce the use of fossil fuels drastically, and also generate no by-products due to the use of energy. For this reason, the secondary batteries are attracting attention as a new environment-friendly energy source for improving energy efficiency.
Generally, an assembly includes a plurality of unit assembly secondary cells, and a battery pack applied to a vehicle or the like includes a plurality of the assemblies or battery modules. The cell includes an electrode current collector, a separator, an active material, an electrolyte, an aluminum thin film layer and the like and allows charging and discharging by an electrochemical reaction among the components.
The battery pack has a problem of low safety while having excellent electrical characteristics. For example, when a lithium secondary battery is used, a decomposition reaction may occur at the components of the battery such as the active material and the electrolyte in an abnormal operation state such as overcharge, overdischarge, exposure to high temperature, short circuit or the like, thereby generating heat and gas. The high-temperature and high-pressure condition caused by the heat and gas may promote the decomposition reaction, which may lead to ignition or explosion.
In particular, when a shock caused by a vehicle collision is applied the battery pack used in a vehicle, the battery pack may be ignited or exploded due to the shock, and the generated fire may lead to a vehicle fire.
To solve this problem, there is a demand for a technology for controlling the output and electric flow of a battery pack so that ignition or explosion does not occur from the battery pack when a collision accident occurs at a vehicle to which the battery pack is applied.